<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        /* li:first-child{
            background-color: aqua;
        }
        li:last-child{
            background-color: yellow;
        } */
        li:nth-child(2n) {
            /*从1开始*/
            background-color: orange;
        }
    </style>
</head>

<body>
    <ul>
        <li>Item 1</li>
        <li>Item 2</li>
        <li>Item 3</li>
        <li>Item 4</li>
        <li>Item 5</li>
        <li>Item 6</li>
        <li>Item 7</li>
        <li>Item 8</li>
        <li>Item 9</li>
        <li>Item 10</li>
    </ul>
</body>

</html>